This application is not referenced in any Microfiche Appendix.
This disclosure is to an improved vortex tube for use in separating an immiscible liquid component from a gas stream and more particularly for a system and a method of operating a system for separating liquid components from a gas stream. An example of an application of the invention is for separating entrained water from a natural gas stream.
The subject of the invention generally relates to gas/liquid separators or gas/liquid/solid separators. Separators of this type are typically process vessels that may be at atmospheric or above atmospheric pressures. The main function of the separator system is to segregate immiscible phases of the process stream such as when the process stream is the form of a gas, such as natural gas that carries with it an immiscible liquid component. The function of the separator of this invention is to separate out the liquid component to provide at the output of the separator a gas stream that is relatively free from entrained liquids.
Separators for separating liquid components from a gas stream are commonly utilized in the oil and gas industry, specifically in oil and gas production, oil refining and gas processing. While very commonly utilized in the oil and gas industry, separators of this type are also used in the mining industry, chemical plants, water treatment facilities, pulp and paper plants and pharmaceutical manufacturing facilities. Separators can be designed to separate a two-phase streamxe2x80x94that is, a vapor/liquid stream or a three-phase streamxe2x80x94that is, a vapor/organic liquid/aqueous stream or a four-phase streamxe2x80x94that is, a vapor/organic liquid/aqueous liquid/solids stream.
Separation of immiscible components of the stream usually and ultimately depend on the force of gravity. Gravity can be either natural gravityxe2x80x94that is, the pull of objects towards the center of the earth or created gravitational forces such as represented by centrifugal separators. Natural gravity is usually used by flowing a stream having immiscible components into a vessel which provides a quiescent zonexe2x80x94that is, a relatively undisturbed environment that allows gravity to act on heavier components of the stream and move them into a downward part of the vessel. This movement has the counteraction of the lighter components of the stream migrating to an upward part of the vessel. In this way, the heavier componentsxe2x80x94that is, liquids, can be withdrawn from the lower part of the vessel and the lighter componentsxe2x80x94that is, gases, withdrawn from an upper part of the vessel.
Another type of gravitational separator utilizes artificial gravity attained by centrifugal force. One way of generating artificial gravity is by the use of a vortex tube. A vortex tube is typically an elongated tube having a cylindrical interior wall that is preferably vertically mounted or at least mounted with a vertically downward tangent. Adjacent an upper end of the vessel is an inlet opening into the vortex tube, the inlet being arranged so that fluids flowing therein tangentially intersect the interior wall of the vortex tube and flow around the interior wall thereby creating centrifugal force that is applied to the components, the centrifugal force serving to move the heavier componentxe2x80x94that is, the liquid component, towards the wall of the vortex tube while the lighter component is forced towards the interior of the vortex tube. In a typical vortex tube the gas is withdrawn from an upper central vortex opening while the liquid component is withdrawn from a liquid outlet in the bottom portion of the vortex tube. The invention herein pertains to improvements to vortex tubes and to methods of using the improved vortex tubes for separation of immiscible components of a gas stream.
For background information relating to the general subject matter of this invention reference may be had to the following previously issued United States patents:
Separators are process vessels, commonly pressurized, which segregate immiscible phases of a process stream. They are commonly used in oil and gas production, oil refining, gas processing, mining, chemical plants, waste water treatment, pulp and paper, and pharmaceutical plants. They separate two-phase streams (vapor/liquid), three-phase streams (vapor/organic liquid/aqueous liquid) or four-phase streams (vapor/organic liquid/aqueous liquid/solids). Separators commonly have an inlet momentum absorber or deflector intended to utilize or reduce fluid incoming momentum, and distribute liquid and gas. This energy reduction initiates phase separation inside the separator vessel. These inlet devices are then followed by various types of de-misting, de-foaming, and/or liquid coalescing apparatus.
The most common separator inlet device is a xe2x80x9csplash platexe2x80x9dxe2x80x94that is, a flat, curved or dished impingement plate that intercepts the incoming flow stream. Fluids are allowed to rebound in a direction considered least destructive to the quiescence of the bulk phases residing in the vessel. Splash plates are characterized by relatively high rebound turbulence. A diffusion inlet is another generic type of inlet device. It typically divides the flow stream into multiple smaller streams and reduces momentum by gradual enlargement of the flow areas of each stream.
The invention herein relates to a xe2x80x9cvortex tubexe2x80x9d that is frequently utilized in a xe2x80x9cvortex tube clusterxe2x80x9d. A vortex tube can be used as a momentum dissipating inlet device and can eliminate other phase separation elements as well. A vortex tube has an inlet through which fluids enter tangentially creating rotational flow. Centrifugal force separates phases within the tube, which then exit, gas from the top through a central gas orifice and liquids from the bottom through peripheral openings. A vortex is formed inside the tube. In a preferred embodiment, the bottom of each tube is submerged below the liquid surface to a depth that prevents the gas vortex from blowing out the bottom.
An essential characteristic of a vortex tube is that it uses flow energy constructively to separate phases whereas in impingement and diffusion devices flow energy is counterproductive to separation, and so they seek to dissipate flow energy as non-destructively as is practical. (xe2x80x9cDestructivexe2x80x9d refers to the tendency of hydraulic agitation to mix, rather than to separate phases). This invention herein includes an improved vortex tube that is usually employed in a vortex tube cluster.
The disclosure herein covers a vortex tube system which produces optimum performance for a variety of process circumstances and conditions.
One improvement described herein minimizes fluid shear by shielding the axially flowing gas stream leaving the top of the tube from the feed stream as it enters the tube tangentially. It consists of a xe2x80x98vortex finderxe2x80x99, which shields the vortex tube outlet stream from disturbance by the inlet stream. It is comprised of a vertical tube the same size as the gas orifice and concentric with the vertical vortex tube and protrudes from the orifice plate on top downward to below the lowest point of the vortex tube entry. This improvement also includes a method of diverting the fluid already rotating circumferentially about the tube as it completes its first rotation from the entering stream. This is done by directing the inlet stream downward using a deflector at such an angle as to miss the tube inlet after one revolution. The deflector diverts the incoming fluid stream downward at the necessary angle. A benefit of using this method is that a smaller amount of liquid mist is carried out of the tube with the gas stream.
Occasionally the gas flow velocity inside a vortex tube may exceed the ideal design limits, either continuously or intermittently due to slugging. This excessive velocity re-entrains liquid mist, and causes the gas stream to spit coarse mist droplets out of the gas orifice. Uncontained, these droplets can result in separator liquid carryover. A second improvement described herein is a method for diverting the gas outlet from the vortex tube downward so that any entrained liquid is directed toward the standing liquid phase. A curved outlet tube is installed on top of the gas orifice to catch these large droplets and direct them harmlessly downward towards the standing liquid. The deflecting tube must arch down sufficiently to create this downward velocity component but does not need to point directly down. If space limits the curve of the tube, it can be modified as shown in FIG. 9. The benefit of this device is that it allows a smaller tube cluster, making the unit more competitive and giving a greater flow turndown to the device without carryover.
In the operation of a vortex tube it is important to control the flow of liquid as it is discharged from the tube bottom. This is done by changing flow directionxe2x80x94that is, to direct the liquid discharge from the tube upward instead of outward by using a tube-on-tube device. This is important if there is any gas carry under from the tube. Gas exiting the bottom of the tube, if allowed to radiate outward, can propel gas-laden liquid towards the liquid outlet, resulting in carry under of gas from the separator vessel. The tube-on-tube design projects this flow upward so that gas more quickly reaches the gas-liquid surface. This tends to keep the gas entrainment localized, allowing a quiet zone in the separator to be more gas-free. The benefit of the tube-on-tube design results in more gas-free liquid leaving the separator.
The liquid release point for a typical vortex tube is located well beneath the liquid surface. However, in low level situations or at start-up, the bottom of the tube may not be submerged. The tube-on-tube arrangement establishes tube-bottom submergence as soon as any liquid is produced. A resulting benefit of incorporating the tube-on-tube system is that during separator startup, or during low liquid level excursions, the vortex tube liquid discharge will remain submerged and will therefore function normally.
Another benefit of the tube-on-tube system is that it keeps disturbance of the oil-water interface more localized around the tube. In three-phase separators the top of the outer tube is typically located below the oil-water interface. An improvement to the tube-on-tube system is the deflector ring. If the liquid release of a tube-on-tube system is near the liquid or interface surface, the deflector ring deflects the upward momentum into a horizontal direction. By the time this deflection occurs, gas has been released and velocity has slowed by natural diffusion. This reduces surface disturbance and phase re-entrainment. The benefit is a reduction in cross-contamination between liquid phases leaving the separator.
To diffuse liquid discharged from a cluster of vortex tubes, a liquid energy absorber may be used that is in the form of a box that surrounds the entire bottom portion of a tube cluster. The box has sides, a top and a bottom, some or all of which are of perforated plate. A liquid energy absorber system reduces turbulent spots in separator liquid residence sections by diffusing vortex tube exit velocities and reduces channeling by improving fluid distribution.
In vertical separators or in large diameter horizontal separators the vertical height of vortex tubes can be significant. When this occurs, liquid separated within the tubes must fall a long distance down the tube wall. As it plunges, gravity accelerates its velocity such that when it finally impinges on the standing liquid, its high momentum re-entrains gas into the liquid phases. Concurrently, in tall vortex tubes, wall friction slows down rotational liquid velocity causing a loss of centrifugal separation as the liquid progresses down the tube. Thus at the bottom of the tube, the liquid velocity direction is nearly vertically downward. To alleviate this problem, a system employing free-fall preventers is used. The benefit of the free-fall preventer system is that gas re-entrainment and foaming are greatly minimized or eliminated, and a higher average g-force is maintained in the vortex tubes to improve phase separation within the tubes.
The claims and the specification describe the invention presented and the terms that are employed in the claims draw their meaning from the use of such terms in the specification. The same terms employed in the prior art may be broader in meaning than specifically employed herein. Whenever there is a question between the broader definition of such terms used in the prior art and the more specific use of the terms herein, the more specific meaning is meant.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.
A better understanding of the invention will be obtained from the following detailed description of the preferred embodiments taken in conjunction with the attached drawings.